The wireless communications network has grown exponentially over the years. A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems, also known as the 4G system, also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). The 3rd generation partner project (3GPP) network normally includes a hybrid of 2G/3G/4G systems. With the optimization of the network design, many improvements have developed over the evolution of various standards. In the 3GPP network where multiple radio access technology (RAT) systems are supported simultaneously, the UE may perform inter-RAT changes. Issues arise when mismatches are found among different systems supported by the same network.
One of the problem is the inter-RAT bearer changes. In the LTE/4G system, the activation of the EPS bearer has less mandatory parameters than the 3G/2G PDP context. Upon inter-RAT bearer changes, if the optional parameters are not presented in the EPS bearer, problems occurs in the new PDP context set up because those parameters are mandatory for the PDP context. In some scenarios, upon detecting the missing of mandatory parameters, the inter-RAT bearer change is terminated. In other scenarios, the behavior was not even defined.
Improvement and enhancement are required for inter-RAT bearer change procedures.